EP1165940B1

EP1165940B1 - Axial dovetail segment for securing a bucket to a turbine wheel and methods of installation

Info

Publication number: EP1165940B1
Application number: EP00907136A
Authority: EP
Inventors: David Alan Caruso
Original assignee: General Electric Co
Current assignee: General Electric Co
Priority date: 2000-02-03
Filing date: 2000-02-03
Publication date: 2007-04-18
Anticipated expiration: 2020-02-03
Also published as: KR20020005646A; KR100785544B1; DE60034440T2; JP4572399B2; EP1165940A1; DE60034440D1; JP2003521622A

Description

TECHNICAL FIELD

The present invention relates to axial entry dovetail attachments between buckets and the wheel of a turbine rotor and particularly relates to an axially inserted dovetail segment for securing the final or closure bucket of a series of axially inserted buckets on a turbine rotor wheel. One such arrangement is shown in US-A-4 904 160 and US-A-3 627 448.

BACKGROUND OF THE INVENTION

Axial entry buckets, i. e., rotor blades, are assembled onto a turbine wheel by sliding the buckets along the rotor axis into mating dovetails on the turbine wheels. In prior assemblies, the turbine buckets have male radially inwardly projecting dovetails for mating engagement with radially inwardly directed female dovetails on the turbine wheel. The wheel dovetails are circumferentially spaced from one another about the wheel. Axial entry buckets on turbine wheels have proven quite satisfactory in assembly and use.
Certain turbine designs, however, require integral covers or shrouds at the bucket tips. Typically the shrouds have overlapping protrusions that nest with shrouds of adjacent buckets. For example, certain shrouds may have, a generally Z-shaped configuration when viewed in a radially inward direction. Should the buckets be assembled serially around the wheel using the axial entry dovetail system, the protrusions of adjacent shrouds, typically the first assembled and next to the last assembled buckets, prevent assembly of the last axial entry bucket from either the upstream or downstream sides of the wheel. The blocking shroud protrusions cannot be removed because the shrouds must be in contact with one another to maintain continuous circumferential coupling of the buckets at their tips in use. Consequently, securing the final or closure bucket with its shroud to the otherwise completed wheel assembly by the axial entry assembly method presents a problem..

BRIEF SUMMARY OF THE INVENTION

According to a first aspect of the invention, there is provided a turbine having a rotor wheel and a plurality of axial entry buckets each securable to the rotor wheel with a first male dovetail which passes through a first female dovetail in the rotor wheel, each bucket including a shroud of the type which nests with the shroud of an adjacent blade to form a continuous circumferential shroud assembly, the turbine characterized by a last-to-be installed bucket assembly comprising an additional bucket configured for attachment to the rotor wheel from a radial direction to permit nesting of an associated shroud with shrouds of adjacent axial entry buckets, said additional bucket including a second female dovetail positioned at a radial inner end such that a second male dovetail, having a complementary shape to the first female dovetail in the rotor wheel, and a complementary shape to the second female dovetail at the radial inner end of said additional bucket, may be simultaneously positioned in the first and second female dovetails to effect attachment of the additional bucket to the rotor wheel.
Preferably, the second male dovetail is a segment body having generally radial opposite male dovetails, one of said dovetails comprising a fir tree configuration including at least two hooks projecting to each side of said segment.
According to a second aspect of the invention, there is provided a method for installing turbine buckets to a turbine rotor wheel where the rotor wheel comprises first axial entry female dovetails spaced one from the other circumferentially about the rotor wheel, each female dovetail configured to receive a single one of a plurality of buckets for attachment to the rotor wheel, each bucket including a shroud of the type which nests with the shrouds of adjacent blades to form a continuous circumferential shroud assembly, the method comprising the steps of providing a second female dovetail on a radial inner end of a last one of the plurality of buckets; providing on a radial inner end of the other ones of the plurality of buckets a first male dovetail with which each of the other ones of the buckets may be attached to the rotor wheel; inserting each male dovetail along an axial direction into the first female dovetail to effect attachment of each of the other ones of the buckets to the rotor wheel; installing said last one of the plurality of buckets against the rotor wheel from a radial direction to permit nesting of an associated shroud with adjacent shrouds of other ones of the buckets; and inserting a second male dovetail in an axial direction into a first female dovetail and into the second female dovetail of the last one of the plurality of buckets to secure the last one (18) of the buckets and the wheel to one another.
Accordingly, it is a primary object of the present invention to provide a bucket to wheel dovetail design for integral shroud covered buckets using axial entry dovetails such that the integrity of the shrouds can be preserved while simultaneously affording radially assembly of the final bucket with its cover completing the circumferentially extending covers about the rotor wheel.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGURE 1 is a fragmentary perspective view illustrating the connections between the buckets and a rotor wheel as well as the axial entrv dovetail segment of the present invention used to secure the final bucket;
FIGURE 2 is a perspective view of the axial entry dovetail segment; and
FIGURE 3 is an end elevational view thereof.

DETAILED DESCRIPTION OF THE INVENTION

Referring now to the drawings, particularly to Figure 1, there is illustrated a portion of a rotor wheel 10 and which rotor wheel 10 forms part of a turbine. Rotor wheel 10 is rotatable about an axis and has a series of female dovetails 12 spaced circumferentially one from the other about the periphery of the wheel. The female dovetails 12 extend axially, i. e., parallel to female dovetails 12 spaced circumferentially one from the other about the periphery of the wheel. The female dovetails 12 extend axially, i.e., parallel to the axis of the rotor wheel and receive mating male dovetails 14 formed on the inner ends of buckets 16. The buckets 16 constitute a series of blades or vanes which are acted upon by the hot gases in the flowpath of the turbine to rotate the rotor wheel. The radial inner ends of the buckets 16 are each provided with the male dovetails 14 which enable axial entry of the buckets to the female dovetails upon assembly of the buckets onto the rotor wheel.
Buckets 16 also include shrouds or covers 18 at their radially outer ends which in final assembly contact one another maintaining a continuous circumferential shroud assembly about the bucket tips. Covers 18 of course rotate with the buckets 16 and rotor wheel 10. The covers 18 as illustrated have a generally Z-shaped configuration as viewed in a radial direction and thus interlock or nest with adjacent covers. While the Z-shaped cover configuration is preferred, there are configurations of covers other than Z-shaped. For example, the covers may have linear angled edges. The particular configuration of the covers is dictated to large extent by the twist and curvature of the buckets 16 which circumferentially offsets the leading and trailing edges of the bucket.
As indicated previously, the male dovetails 14 of the buckets 16 are inserted axially into the female dovetails 12 during assembly of the buckets to the rotor wheel. Thus, buckets 16 are assembled serially around the wheel. For example, a first bucket 16a is assembled to the rotor wheel 10 by axially displacing the male dovetail 14a into the female dovetail 12a. The next bucket 16b is similarly assembled to the rotor wheel 10 by axially displacing the male dovetail 14b into the female dovetail 12b of the rotor wheel. It will be appreciated that the covers 18a and 18b on the bucket 16a and 16b respectively nest with one another upon such axial entry. Additional buckets are secured to the rotor wheel in like fashion serially about wheel 10 and eventually the next to the last bucket 16x is installed on the rotor wheel 10 by inserting the male dovetail 14x into the female dovetail 12x. Thus it will be appreciated that the buckets, save for one final bucket, are axially inserted into and completely installed about the rotor wheel with the covers 18 in nesting relation relative to one another. However, from a review of Figure 1 it will be appreciated that the final or closure bucket 16y cannot be inserted relative to the rotor wheel from either axial direction because the cover 18y cannot pass through the openings defined by the adjacent covers 18a and 18x. Consequently, a different type of connection and assembly procedure is required to install the final bucket 16y onto the rotor wheel 10.
To accomplish this, instead of providing the final bucket 16y with a male dovetail similar to the male dovetails 14 at radial inner ends of the other buckets 16, the final bucket 16y is provided with an axially extending female dovetail 20 along its radial inner end. Additionally, as best illustrated in Figure 2, an axial entry dovetail segment 22 is provided for joining the final bucket 16y to the rotor wheel 10 at the female dovetail connection 12v. It will be appreciated that the dovetail connection 12y is identical to the dovetail connections 14 spaced circumferentially about the rotor wheel 10. The axial entry dovetail segment 22 includes male projecting dovetails 24 and 26 along radially opposite sides of the segment, the segment extending axially a distance corresponding to the axial length of the male dovetails on the buckets 16. The radial innermost male dovetail 24 on segment 22 has a generally complementary shape to the female dovetail 14y; whereas the radially outer male dovetail 26 on segment 22 is generally complementary in shape to the female dovetail 20 of the final bucket 16y. By employing the axial entry dovetail segment 22 the final bucket 16y can be assembled from a radial direction and positioned between the first bucket 16a assembled to rotor wheel 10 and the next to the last bucket 16x assembled to rotor wheel 10. It will be appreciated that by radially inserting the bucket 16y, the radially inner base of the bucket is readily disposed between the radial inner bases of the adjacent buckets 16a and 16x. Additionally the cover 18y of final bucket 16y nests between the covers 18a and 18x of the adjacent buckets. To secure the final or closure bucket 16y to the rotor wheel 10, the axial entry dovetail segment 22 is driven axially such that the male dovetails of the segment respectively engage in the female dovetails of the final bucket 16v and the rotor wheel 10.
Referring to Figure 2, the geometry of the radially inner male dovetail 24 of the segment 22 is the same as the female dovetails 12 on the rotor wheel. That is, the hooks 25 of the dovetails are substantially complementary to one another. Similarly, the radially outer male dovetail 26 of segment 22 is complementary in shape to the female dovetail on the final or closure buckets 16y. That is, the hooks 27 of the male dovetail are substantially complementary to the hooks of the female dovetail. Note also that the protrusions or tangs 28 on the segment 22. These tangs 28 provide tangential restraint in the mating final or closure bucket female dovetail. Hooks 25 and 27, of course, engage corresponding hooks in the wheel dovetail and the final bucket female dovetail in final assembly.
While the invention has been described in connection with what is presently considered to be the most practical and preferred embodiment, it is to be understood that the invention is not to be limited to the disclosed embodiment, but on the contrary, is intended to cover various modifications and equivalent arrangements included within the scope of the appended claims.

Claims

A turbine having a rotor wheel (10) and a plurality of axial entry buckets (16a, 16b; ...16x) each securable to the rotor wheel (10) with a first male dovetail (14) which passes through a first female dovetail (12) in the rotor wheel, each bucket including a shroud (18) of the type which nests with the shroud (18) of an adjacent blade to form a continuous circumferential shroud assembly, the turbine characterized by a last-to-be installed bucket assembly comprising an additional bucket (16y) configured for attachment to the rotor wheel from a radial direction to permit nesting of an associated shroud (18) with shrouds of adjacent axial entry buckets, said additional bucket including a second female dovetail (20) positioned at a radial inner end such that a second male dovetail (22), having a complementary shape (24) to the first female dovetail (12) in the rotor wheel, and a complementary shape (26) to the second female dovetail (20) at the radial inner end of said additional bucket, may be simultaneously positioned in the first and second female dovetails (12, 20) to effect attachment of the additional bucket (16y) to the rotor wheel (10).
A turbine according to claim 1, wherein the second male dovetail is a segment body (22) having generally radial opposite male dovetails (24, 26), one of said dovetails (24) comprising a fir tree configuration including at least two hooks projecting to each side of said segment.
A method for installing turbine buckets to a turbine rotor wheel (10) where the rotor wheel (10) comprises first axial entry female dovetails (12) spaced one from the other circumferentially about the rotor wheel (10), each female dovetail (12) configured to receive a single one of a plurality of buckets (16a, 16b, ...16x, 16y) for attachment to the rotor wheel (10), each bucket including a shroud (18) of the type which nests with the shrouds (18) of adjacent blades to form a continuous circumferential shroud assembly, the method comprising the steps of:
providing a second female dovetail (20) on a radial inner end of a last one (16y) of the plurality of buckets;

providing on a radial inner end of the other ones of the plurality of buckets (16a, 16b, ...16x) a first male dovetail (14) with which each of the other ones of the buckets may be attached to the rotor wheel (10);

inserting each male dovetail (14) along an axial direction into the first female dovetail (12) to effect attachment of each of the other ones of the buckets to the rotor wheel (10);

installing said last one (16y) of the plurality of buckets against the rotor wheel (10) from a radial direction to permit nesting of an associated shroud (18) with adjacent shrouds (18) of other ones of the buckets; and

inserting a second male dovetail (22) in an axial direction into a first female dovetail (12) and into the second female dovetail (20) of the last one of the plurality of buckets to secure the last one (18) of the buckets and the wheel (10) to one another.